New Jersey Gov. Chris Christie (r.) wearing an Arsenal scarf, sits with Rutgers University President Robert Barchi during the English Premier League soccer match between Arsenal and Aston Villa at the Emirates stadium in London, Feb. 1, 2015. Christie, a likely Republican candidate for president, said Monday that parents should have some choice on whether to vaccinate their children.

With the most recent measles outbreak, fears about the disease are rising, as are calls for tougher vaccination laws. Politicians – including presidential hopefuls such as former Secretary of State Hillary Rodham Clinton (D), New Jersey Gov. Chris Christie (R), and Kentucky Sen. Rand Paul (R) have weighed in.

The actual number of diagnosed measles cases is still tiny, but is greater than in the recent past, and have some concerned that a disease thought to be eradicated could be returning.

Here are some of the facts, both about the most recent measles outbreak and vaccination:

Those numbers are minuscule in the context of the US population, but high when compared with recent years, especially since the CDC declared measles eliminated in 2000 (meaning that year-round, endemic transmission doesn’t occur anymore). Between 2001 and 2010, a median of about 60 cases was reported each year. However, last year a spike in numbers was reported, with 644 cases. Many of those were linked to travelers returning from the Philippines, and there was also a large outbreak among Ohio Amish communities.

For many people, measles is a relatively minor disease, but for some – especially the very young and medically fragile – it can be serious. According to the CDC, about 28 percent of young children who are diagnosed with measles need to be treated in the hospital, and for every 1,000 children who get measles, between one and three die.

But to put it into perspective, in 2011 more than 50,000 Americans died from influenza and pneumonia, while measles has been virtually eliminated as a cause of mortality in the US. (Globally, it remains one of the leading causes of death among young children, according to the World Health Organization.) Before the introduction of the measles vaccination program in the 1960s, the US had more than 500,000 cases of measles reported annually, and about 450 measles-related deaths each year.

How extensive is vaccination in the US?

According to the most recent CDC data, about 95 percent of children have been vaccinated for measles, mumps, and rubella (MMR). Compliance varies by community and by state, though. Rates vary from about 82 percent of children in Colorado to nearly 100 percent in Mississippi.

The number of waivers – exemptions from the CDC vaccine schedule sought by parents for medical, religious, or “personal belief” reasons – also vary significantly by state, from less than 0.1 percent in Mississippi to 7.1 percent in Oregon.

According to Mark Largent, a historian at Michigan State University in East Lansing and the author of "Vaccine: The Debate in Modern America," vaccine compliance is currently at an all-time high, as are the numbers of vaccine waivers on file.

How to reconcile those two seemingly contradictory statistics? Districts are getting more vigilant about pushing families to either be compliant or get the official waiver, says Professor Largent. In the past, there was a large “third category” of kids whose parents simply didn’t get them to the doctor or forgot about vaccines. More of those families are being pushed to be compliant in some form.

“As much as we worry, the high waiver rate is actually a barometer for how much attention is being paid to the vaccination debate,” says Largent.

Largent and others also note that waivers shouldn’t be taken as a proxy for non-vaccination, since children with waivers actually have many of their shots. The parents might be opting for a slightly different schedule, or, in some cases where the exemptions are easy to obtain, see signing one as easier than getting their doctor to sign off on the vaccination form.

“These are not anti-vaccine people,” says Largent. “Almost all of their kids have some vaccines. They’re saying we don’t accept the size of the current vaccine schedule.”

What are the laws governing vaccination?

All states have vaccination requirements for children to attend school, but they all also offer at least some form of exemption. Parents can seek a medical exemption in all 50 states, and in all but West Virginia and Mississippi they can seek a religious exemption. Some 20 states also have philosophical exemptions available. It varies, though, how easy these waivers are to obtain, and in recent years, some states have sought to make the process both easier and harder.

In Washington, California, and Vermont, for instance, parents seeking an exemption now must get a doctor’s signature. And Michigan just passed a law that parents who want a waiver must first be educated by a health worker about vaccines and the diseases they prevent, and must sign a form that they understand they may be putting their children and other children at risk.

Who chooses not to vaccinate

While recent reporting has emphasized vaccine opt-outs in affluent, educated, liberal communities such as Marin County and parts of Orange County in California – parents who are committed to a more natural lifestyle, arm themselves with their own research, and tend to be skeptical of pharmaceutical companies – vaccine skepticism actually cuts across ideological, religious, and class lines.

Some religious communities – including Amish, Orthodox Jewish, and Christian Science communities – have some members who seek religious exemptions. Some parents on the right are as skeptical of government mandates as those on the left are about pharmaceutical companies, and there are vaccine conspiracy theories on both the right and the left.

The most sensitive vaccination topic involves those individuals who can’t be vaccinated for medical reasons – which also may make them more at risk for complications – or babies who are too young. Much of the anger at non-vaccinators involves the fact that they may be increasing the risk to these vulnerable populations.

In recent days, several Republican politicians, including Governor Christie and Senator Paul, made statements that seemed to give support to parents who choose not to vaccinate their children (Christie's staff later clarified his comment), but the reality is that there is little partisan difference on the issue. A 2014 Pew study found that 65 percent of Republican voters believed vaccines should be required, compared with 76 percent of Democratic voters. Other studies have found no partisan gap at all.

“Democrats and Republicans agree, vaccination is good,” says Brendan Nyhan, a political scientist at Dartmouth College in Hanover, N.H.